After 23 years on defense, veteran Federal Defenders lawyer Deirdre von Dornum is itching to play offense.

The longtime public defender — known as a smiling legal gladiator who’s won rare acquittals in a federal system where prosecutors prevail at trial 90% of the time — is making the move to the Manhattan-based law firm Sher Tremonte to fight the Trump administration over immigration and First Amendment cases.

“I couldn’t sit still and watch President Trump and his DOJ intimidate protesters, professors, prosecutors with ethics, even judges carrying out their constitutional duties. If there is one thing I’m good at, it’s getting in the government’s way,” von Dornum tells the Daily News.

“I intend to use that skill to ensure dissent is not silenced.”

The 56-year-old litigator is joining Sher Tremonte, a litigation boutique firm, that, most recently, represented the plaintiffs in a case challenging the Trump administration’s efforts to deport noncitizen college students and faculty, like Columbia University grad student, Mahmoud Khalil, who take part in pro-Palestinian protests.

Massachusetts Federal Court Judge William Young ruled for the students last month in a blistering opinion that blasted Trump for ignoring the law and the Constitution.

Von Dornum said she hopes to pursue similar cases.

“I’m making (the move) so I have more freedom to take on cases against the administration, not just do reactive criminal cases,” she said.

Von Dornum, a Columbia University Law School graduate who clerked for Supreme Court Justice Ruth Bader Ginsburg, served as the Federal Defenders Attorney-in-Charge of the Eastern District of New York, recently stepping down from that top spot to represent clients full-time.

She’s so well regarded in her field that Juliana Margulies shadowed her for several days to prepare for her defense attorney character on “The Good Wife.”

“There is nothing more unsettling to a lawyer than a smiling adversary, and Deirdre has hard-earned confidence, intelligence and experience behind her smile,” said former Brooklyn U.S. Attorney Seth DuCharme. “She has a genuine enthusiasm for litigation.”

Von Dornum led the charge against horrific conditions at the MDC Brooklyn jail, pressing federal Bureau of Prisons officials during an eight-day blackout in the dead of winter 2019, after a flood of complaints about no heat, noxious fumes and no electricity. Jail officials kept suspending legal visits and claiming that the lights and heat were still on, leading a federal judge in Brooklyn to send von Dornum into the jail to see for herself what was going on.

“What started our MDC litigation was just a flat-out lie of, ‘The lights are on, the heat is on.’ And we were standing there in the freezing cold and dark,” she said.

Von Dornum was also part of the team that challenged Boston Marathon bomber Dzhokhar Tsarnaev’s death sentence, and considers the ruling to overturn the sentence one of her career highlights. Though the Supreme Court upheld the death sentence in 2022, Tsarnaev’s fate remains up in the air after an appeals court ordered a probe into claims of jury bias last year.

She credits Ginsburg’s lessons about attention to legal detail as what led to her first breakthrough in the appeals process, when she noticed skipped numbers on the docket.

“I saw the power not just of strong beliefs, but of making really careful legal judgments and writing really tightly so that it can’t be undone,” von Dornum said of Ginsburg. “I was really amazed by her ability to go piece by piece, so that it could never be changed.”

Former Assistant U.S. Attorney and former Deputy Assistant Attorney General Nicole Argentieri said von Dornum is also willing to build relationships with prosecutors and federal agents, despite sitting at the defense table.

“Even though there were times we were adverse and she was tough, she was very practical and willing to work through issues where we could. She picks the fights that matter, not every fight,” she said.

One of those fights was the trial of Thomas Welnicki, 75, who was accused of threatening to kill President Trump in a series of rambling phone calls to the Secret Service in 2021.

In an argument that included lyrics from the John Lennon song, “Imagine,” von Dornum said Welnicki wasn’t making actual threats — he was simply sad, drunk and lonely while cooped up in his Queens apartment during the pandemic and the Secret Service were the ones to take his calls.

The jury acquitted Welnicki, who three years later calls von Dornum “an angel” and a “warrior woman.” Welnicki, who goes by the nickname Knicky Knightrow, stays in touch with her, sending her classic rock playlists.

“She’s a very strong advocate for the rights in a courtroom of people who are accused of crimes, as it should be,” Welnicki tells the news. “She has a passion for truth, honesty, justice and the American way.”

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